need cam advice from 351 guys

[82 GT]

I'm just wondering what cam grinds you guys are running in your modified 351w.
I currently rebuilding a 351w in my '82GT and am looking for a good street cam. I want something with a rough idle but still streetable(if that's possible)
I be using a C-4 with stall converter, 3:73 gears, 625 carter carb and 10:1 compression.
I was thinking of the COMPETITION CAMS 292* .512/.512 lift
(244* @.050)
Would that be too much for mostly street use?
I was also considering their 280* .501/.501
(230* @.050)
BTW, it's a '74 351w and I'll be using the '69 heads
I realize that cam selection can is critical so I want to make a good choice for my application.

[Shaggy]

With the 69 heads you are going to want a cam that favors the exhuast not a single pattern like yu have used for examples... How much are you polanning on spending? I would suggest converting to roller using the comp cams conversions rollers with a tie bar they will allow you to run any of the "new" roller grinds regardless of if it is a small base circle conversion cam or not. and for off teh shelf cams to price i would say the stage 2 oe 3 trick flow cam depending on how radical you are going to get with it.

[82 GT]

I would like to go roiller but I don't have the cash for that.
I'll keep inmind the duel profile grinds like you mentioned.
I also heard that engine with poor heads tend to favor a wide LSA angle. What size lift would be tha max for stock iron heads to make the most use of?

[Rev]

Comp Cams makes the Extreme Energy line that I believe are dual pattern cams. Personally, I wouldn't go over 280 advertised duration for the street, even with the gears and stall. You might want to call the tech line for their advice on the matter.

Rev

[82 GT]

Originally posted by Rev
.Personally, I wouldn't go over 280 advertised duration for the street, even with the gears and stall. You might want to call the tech line for their advice on the matter.

Rev

Uh oh......Maybe I should have waited for some more replies before I ordered my cam today.
I ordered one from Crower Cams and the specs are:

298*/304* duration
224*/234* @.050
.498/.520 lift
112* LSA

The power range claims to be between 1750-6000 rpms but those numbers don't seem to indicate.(at least not to me)
I was thinking that the lift on the intake side was pretty decent and the extra lift on the exhaust would be a wise choice like
shaggy recommended.

Is this cam still a good choice or is that way..way too much duration?
What do you think the idle quality will be like? I did want a racey idle.

[Rev]

There is some leeway in the way manufactuors measure "advertized duration". I think the best way is to compare duration at .050" lift. Sometimes, advertized duration is manipulated to give higher numbers because that seems to be what some people want. What some manufacturers do is to start the ramp earlier and end it later, but at miniscule amounts to artificially raise the "duration".

The 224/234 @ .050" numbers tell me this is exactly what Crane did. As a comparison, my 268 HE from Comp Cams is 218/218 @ .050". So I'll bet your still OK if a max street cam is what you're after. It might compare to another cam advertized as 280/290 or something like that.

Rev

[hobgoblin351]

When I first saw the 298*/304* I thought wway to big for the street. But at .050 with the 224*/234* it seems more street friendly. That and the lift is not really that high. I'd stick with it. Anything bigger at .050 and you start to really push the streetable boundries. Hindsite being 20/20, I probably should have bumped mine down a notch, but hey I'm getting used to it!

[Shaggy]

Sorry to take so long to jump back in so late... those specs look almost exactly like a cam i was running about 10 years ago only real difference wwas mine was 110 centers. That cam should pull real hard to 6 and beyond if you have the heads intake and exhaust fot it. It is a rough cam tto use on the street but i liked it but I am not most people(I also run a spool on the street in my daily driver) I personally like "high" lift cams on the ported stockers... If it was a customers car i would have gone with a little less duration though. My personall opionon on lift for a 351 is if it ain't at least .500 then it is still a "mild" cam.. I know that will stir all kinds of crap up so let me say my reasons before everbody starts to go off on that last statement.

Ok a good set of ported stockers will flow to about .600 before steadying out or even loseing a little, with that in mind even if the port job onm your heads isn't that good at it only flows good to about .500 or even say a real extreme example .400 okay well if yyour peak flow is at .400 then you want the valve to be at .400 as long as possible correct? Welll if you buy a cam tha has .400 lift then the valve only see s that area around .400 once per revolution now if you say get a cam that has .500 lift on the same motor then the valve will see the .400 are once as it opens and once as it closes so twice during a revolution. remember if you peak is at .400 then what you are going to probaly really going to have for best best flow on average (not peak) will be say .350 to .450 with the .400 cam your valve would ever really see any of the good flow above .400...... Kinda like a torque/HP curve and the reason most combinations run faster if you actually shify a little after there peak HP.

[Rev]

Yes, Shaggy is right here. We want peak flow at around .5 valve lift for an agressive street cam. I think that's what we are tying to say? Any other input is welcome.

Rev

[82 GT]

What makes a cam have a "rough" idle? Is it a wide LSA or duration?
Is my cam going to have a rough idle because that's what I want.
I tried to pick something with specs that would fit my engine combo and yet still have a nice rough idle.
shaggy , would you consider this a "mild" cam or a borderline "radical"cam?

[Shaggy]

For the "average" user i would consider it more towards the radical side.... (to a "hardcore" jot rodder it is a nice street cam)It should idle plenty rough... Typically the longer the duration the rougher the idle but if you have 2 cams with the same duration but one is on tighter centers then it will idle rougher then the wider one and same thing for 2 cams with the same lobe seperation and different durations the longer duration cam will ridle rough....but duration has more to do with idle quality than lobe center does in my expierence.

[hobgoblin351]

This feels like a refresher course on cam science. I like it! Shaggy I remembed that the idle quality is effected by the duration. Now the lobe seperation, if I'm not mistaken , is tied to overlap and effects the RPM range of the cam?

[Shaggy]

[disclaimer] Thes next few state are VERY general generilazations and not the end all to cam science unfortuantly cam generalizations are very vague at best since there is a lot more involved then just one or 2 items like we have been discussing[/disclaimer]

Now the lobe seperation, if I'm not mistaken , is tied to overlap and effects the RPM range of the cam?

This statement is mostly true, for a cam with the same lift and duration specs a cam with a tighter lobe cylinder will generally prvide more cylinder pressure and create a lower rpm for peak power but it generally higher peak torque number BUT at the expense of making a very narrow power band while the cam with a wider lobe seperation will generally blead more cylinder pressure off but provide a much wider power band wiith typically a higer peak hp rating at a slightly higher rpm than one with a tighter lobe seperation. The problem with stating the above statement is that depending on combonation you make more power with one cam that has 110 centers but with different lift and/or duration than aother cam with say 112 centers. While we are talking a generalizations a cam with a tighter lobe seperation will promote higher cylinder pressures because of where the piston is when the valve actually closes..

Genreally what i like to do is on a low compression pump gas motor is run 110 to 112 centered cam. On a low compression race gas motor is run a 108 to 110 centered cam and on a high compression pump gas motor is run a 112 to 114 and on a high compression race gas motor run a 110 to 112. The above lobe center recommendations are a very rough guideline for NA and gearing the car after makin a cam selection. Which is a point we haven''t even really brought up yet is gearing.

Generaly speaking I like to pick a cam that matchs the rest of the motor combination so as to make the most usable power (My definiton of usable power) and then gear the car accordingly.

[82 GT]

Originally posted by Rev
There is some leeway in the way manufactuors measure "advertized duration". I think the best way is to compare duration at .050" lift. Sometimes, advertized duration is manipulated to give higher numbers because that seems to be what some people want. What some manufacturers do is to start the ramp earlier and end it later, but at miniscule amounts to artificially raise the "duration".

The 224/234 @ .050" numbers tell me this is exactly what Crane did. As a comparison, my 268 HE from Comp Cams is 218/218 @ .050". So I'll bet your still OK if a max street cam is what you're after. It might compare to another cam advertized as 280/290 or something like that.

Rev

Rev , made an interesting statement there. How can two cams with similiar lifts @.050 have very different advertised durations?
Do you mean it's possible that my duration isn't really 298*/304*
only because Crower Cams and other cam companys are trying to sell people what we think we want in terms of duration?
In other words, are two cams with the same duration @.050, the same lifts and the same same lobe centers actually the same cams regardless of "advertised" durations?
I guess it's best to pick a cam based on specs @.050 and ignore advertised durations and lifts.
If that's true then that's how people get confused when it comes time to pick a cam because "adertised" specs and .050 specs are like the Metric system and English system.
Mosy people relate better to "advertised" specs(English system) better than the .050 specs(Metric system)
Would that be an acurate analogy?

This is an interesting class we are having here!

[Shaggy]

Not so much the metric and and english system as much as a way to inflate numbers Here is a graph i just made to try and help explain it.

Full camlobe

Okay in this graph I mapped 2 different lobes both starting at 0 at both going to a max lift of .490 (since that is the inttake lift on your cam). It only is a 9 point graph so it isn't precise or anything to say this is your cam. In the example graph you see at .050 both graphs are at the same xy point but right after that they get a whol lot different... we are actually only converned about the area before .05 though for this discussion. which is illistrated here,

under .05 camlobe

Now i drew this in a linear fashion instead of a curve I am getting to tired to draw it fully correct as a proggesive curve, but you see that goes for 0 to .05 for 9 steps if we say the that is 9 degrees (one per point) then there is one that has 9 degrees of duration and one that only has 8 degrees of duration yet they both end up at .05 by 9 total degrees. The p[roblem is that with any thing under .05 is it is such a small difference that it is really negliable.



more tomorrow.

[82 GT]

shaggy , here are the detailed specs of my cam:

INTAKE

Opens: 4.0 BTDC
Closes: 40.0 ABDC


EXHAUST

Opens: 53.0 BBDC
Closes: 1.0 ATDC


LOBE SEPERATION

112º


Duration at .050"

Intake: 224
Exhaust: 234


LOBE LIFT

Intake: 0.311
Exhaust: 0.325

[Shaggy]

Cool i woll lok closer at it at home tonight...l

[Shaggy]

What cam part number is that? I am sitting here at work making good use of my time and i was mapping your cam out as best i can with the numbers you gave me but they are not adding up quite right. I also do you have a degree wheel? if you do i can edit the map after you install it if you take several measurement of lift versus degrees i should be able to map out you ramp rate as well.

[82 GT]

The part # is 15903 from crower.com

No, I don't have a degree wheel. Does degreeing a cam make that much of a difference?
I'm still waiting on my cam to get here. It's supposed to be here Friday.
If you think degreeing the cam will make much of a difference for me then I'll consider buying a degree wheel. I was just going to install it "straight up".

[Shaggy]

I have installed several without degreeing them. Most cams and timing sets nowadays are accurate enough that degreeing them has almost become obsolete... I say almost because I still check degree everything but street motors and rarely do I find one that is off. If you had a degree wheel and a mic I could make an accurate lobe map of your cam that would show your ramp rate as well as the specs given to you by crower.